Add export command and shared item tree

Introduces a pure, FUSE-independent item tree (buildItemTree) shared by the mount and export commands. The new export subcommand downloads Docspell search results into a local directory, mirroring the mount's friendly folder/year/month hierarchy without the by-id directory or metadata JSON file, for archival or migration.

- itemtree.go: pure item tree builder shared by mount and export
- mount.go: buildMountTree now converts the pure tree into FUSE nodes, with a shared fileNode per attachment across friendly and by-id paths
- export.go: export command with concurrent downloads, --dry-run, --skip-existing, --concurrency, --query, --limit, --auth-header
- main.go: wires up the export subcommand and its flags
- export_test.go: tests for plan collection, writes, skip-existing, failures, modtime
- README.md: documents the export command

main.go

@@ -60,6 +60,12 @@ func main() {
 			fmt.Fprintln(os.Stderr, "mount failed:", err)
 			os.Exit(1)
 		}
+	case commands.exportCommand.Used:
+		cfg, password := loadConfigAndPassword()
+		if err := runExportCommand(os.Args[2:], cfg, password); err != nil {
+			fmt.Fprintln(os.Stderr, "export failed:", err)
+			os.Exit(1)
+		}
 	case commands.getPathCommand.Used:
 		cfg, password := loadConfigAndPassword()
 		if err := runGetPathCommand(os.Args[2:], cfg, password); err != nil {
@@ -80,6 +86,7 @@ func main() {
 type cliCommands struct {
 	importCommand  *flaggy.Subcommand
 	mountCommand   *flaggy.Subcommand
+	exportCommand  *flaggy.Subcommand
 	getPathCommand *flaggy.Subcommand
 	getURLCommand  *flaggy.Subcommand
 }
@@ -93,28 +100,40 @@ func newCLIParser() (*flaggy.Parser, cliCommands) {
 	commands := cliCommands{
 		importCommand:  flaggy.NewSubcommand("import"),
 		mountCommand:   flaggy.NewSubcommand("mount"),
+		exportCommand:  flaggy.NewSubcommand("export"),
 		getPathCommand: flaggy.NewSubcommand("get-path"),
 		getURLCommand:  flaggy.NewSubcommand("get-url"),
 	}
 	commands.importCommand.Description = "Scan configured import folders, archive confirmed files, and optionally upload missing files"
 	commands.mountCommand.Description = "Expose Docspell search results as a read-only FUSE filesystem"
+	commands.exportCommand.Description = "Download Docspell search results into a local directory, mirroring the mount hierarchy"
 	commands.getPathCommand.Description = "Resolve a Docspell item ID or URL to the local mounted path"
 	commands.getURLCommand.Description = "Resolve a local mounted path, item ID, or item URL to a Docspell web URL"
 
 	var uploadMissing bool
 	commands.importCommand.Bool(&uploadMissing, "", "upload-missing", "true, to upload files to docspell that do not yet exist there")
-	var query, mountPoint, itemIDOrURL, pathOrID string
+	var query, mountPoint, exportDest, itemIDOrURL, pathOrID string
+	var exportConcurrency int
+	var exportDryRun, exportSkipExisting bool
 	authHeader := defaultDocspellAuthHeader
 	limit := 1000
 	commands.mountCommand.String(&query, "", "query", "Docspell item query to expose")
 	commands.mountCommand.Int(&limit, "", "limit", "number of items to fetch per API request")
 	commands.mountCommand.String(&authHeader, "", "auth-header", "HTTP header used for the Docspell auth token")
 	commands.mountCommand.AddPositionalValue(&mountPoint, "mountpoint", 1, false, "mount point, overriding mountPath from config")
+	commands.exportCommand.String(&query, "", "query", "Docspell item query to expose")
+	commands.exportCommand.Int(&limit, "", "limit", "number of items to fetch per API request")
+	commands.exportCommand.String(&authHeader, "", "auth-header", "HTTP header used for the Docspell auth token")
+	commands.exportCommand.AddPositionalValue(&exportDest, "destination", 1, false, "destination directory for the export")
+	commands.exportCommand.Int(&exportConcurrency, "", "concurrency", "number of attachments to download in parallel")
+	commands.exportCommand.Bool(&exportDryRun, "", "dry-run", "print the files that would be written without downloading")
+	commands.exportCommand.Bool(&exportSkipExisting, "", "skip-existing", "skip files that already exist in the destination")
 	commands.getPathCommand.AddPositionalValue(&itemIDOrURL, "item-id-or-url", 1, true, "Docspell item ID or web URL")
 	commands.getURLCommand.AddPositionalValue(&pathOrID, "local-path-or-item-id", 1, true, "local mounted path, item ID, or item URL")
 
 	parser.AttachSubcommand(commands.importCommand, 1)
 	parser.AttachSubcommand(commands.mountCommand, 1)
+	parser.AttachSubcommand(commands.exportCommand, 1)
 	parser.AttachSubcommand(commands.getPathCommand, 1)
 	parser.AttachSubcommand(commands.getURLCommand, 1)
 	return parser, commands